Structural instabilities and mechanical properties of U2Mo from first principles calculations

Area of Science:

• Materials Science
• Computational Materials Science
• Solid State Physics

Background:

• Uranium-Molybdenum (U2Mo) alloys are critical nuclear materials.
• Understanding their mechanical properties is essential for safe and efficient applications.
• Previous theoretical studies on U2Mo structure and stability have yielded conflicting results.

Purpose of the Study:

• To perform first-principles calculations on the structural and elastic properties of U2Mo with the C11b structure.
• To investigate the mechanical and dynamic stability of the I4/mmm phase.
• To determine the ideal tensile and shear strengths of U2Mo.

Main Methods:

• Density Functional Theory (DFT) based first-principles calculations.
• Analysis of elastic constants and phonon dispersion relations.
• Calculation of ideal strengths under tensile and shear loading.

Main Results:

• The I4/mmm structure of U2Mo is confirmed to be mechanically and dynamically unstable.
• Negative elastic constant C66 and imaginary phonon modes indicate instability.
• U2Mo exhibits significantly lower ideal shear strength (8.1 GPa) compared to tensile strength (18-28 GPa).

Conclusions:

• The I4/mmm phase of U2Mo is unstable, contradicting some prior theoretical work.
• U2Mo is predicted to fail primarily through shear rather than tensile stress.
• These findings are crucial for the design and application of U2Mo nuclear fuels.